The invention relates to a rotary anode comprising a basic body of carbon whose surface is provided with a coating of pyrolytic graphite having a crystallographic layer structure on which there is provided a further metallic layer of a high-melting temperature in which X-rays are generated during operation in an X-ray tube. The invention furthermore relates to a method of manufacturing such a rotary anode, in which a coating of pyrolytic graphite is deposited on the surface of a basic body of carbon, and a further metallic layer of a high-melting temperature is deposited on the coating of pyrolytic graphite.
A rotary anode of the kind set forth is known from German Offenlegungsschrift No. 21 46 918. The pyrolytic coating thereof serves to obtain smooth surfaces which are free of pores, so that no particles can become detached from the basic body. Due to the absence of pores, the so-termed "after-gasing" is prevented, so that a permanent high vacuum can be comparatively easily maintained. The pyrolytic coating on the basic body of the known rotary anode is deposited by means of known methods. The basic body is heated to a temperature of from 500.degree. to 1200.degree. C. and at the same time a gaseous carbon compound is guided across the basic body, so that carbon is deposited on the basic body.
From German Offenlegungsschrift No. 17 71 980 which corresponds to U.S. Pat. No. 3,410,746, it is known that, when pyrolytic graphite is deposited on a surface from the gaseous phase, the deposited layer exhibits a crystallographic layer structure whose crystal faces generally extend parallel to the surface and parallel with respect to each other. The thermal conductivity of the graphite is much higher in the direction of the crystallographic layers than in the direction transversely thereof. This means that the layer of pyrolytic graphite which is known from German Offenlegungsschrift No. 21 46 918 is less than optionally suited for conducting heat from the layer of high-melting temperature metal to the basic body, because the crystallographic layers in the pyrolytic graphite follow the circumference of the basic body.